MINNEAPOLIS (AP) — Investigators from the National Transportation Safety Board arrived at a Minneapolis school on Thursday to begin the painstaking task of determining what caused an apparent natural gas explosion that killed two people and injured at least nine others, including one critically.City fire officials said the collapse was caused by a natural gas explosion in a utility area.Experts said the investigation will take time and include interviewing witnesses, including employees from Master Mechanical Inc.Questions will include what type of work was being done, whether the building should have been occupied at the time, if all precautions were taken to make sure it was done safely, and whether the contractors should have isolated the natural gas source before proceeding, Farley said.Jenny O'Brien, a spokeswoman for Minnesota Occupational Safety and Health Administration, said in 2010 the company was fined for a violation related to protecting an employee from falling.Three people remained hospitalized Thursday, including an assistant soccer coach who was in critical but stable condition, according to Hennepin County Medical Center.

Amazon.com Inc. is looking to fill more than 50,000 jobs in a hiring spree at 10 warehouses . The Seattle company is planning to make thousands of offers on the spot at the locations on Wednesday.The warehouses holding job events are:— Baltimore— Chattanooga, Tennessee— Etna, Ohio— Fall River, Massachusetts— Hebron, Kentucky— Kenosha, Wisconsin— Kent, Washington— Robbinsville, New Jersey— Romeoville, Illinois— Whitestown, IndianaIn addition, Amazon is seeking candidates for part-time positions in Oklahoma City and Buffalo, New York.